1. Field of the Invention
The invention relates to a record carrier having compressed audio programs recorded on a track thereof, and to a recording method and apparatus for recording audio programs on a track of a record carrier.
2. Description of the Related Art
The compact disc (CD) digital audio that was invented in the 1980s is a good media for digitally recording stereo audio information with high fidelity. The advantages of using digital technology to represent audio and video signals are apparently known in the art. Aside from the benefit of good quality when audio and video signals are recorded digitally, the manufacturing cost of CD media has become cheaper in recent years, thereby facilitating the progress of digital recording for audio and video signals.
Recent advancements in the field of video compression have made it possible to record video signals in CD media. A video CD with the same physical structure as the CD digital audio was proposed by adopting Motion Pictures Expert Group (MPEG) compressed video and audio to record a total of 74-minute length programs on a CD medium. The bit rate of compressed video is about 1.15 Mbits/sec, while that of compressed audio is about 224 Kbits/sec. These bit rates are designed for accommodating the constant linear velocity of the CD drive of a playback apparatus, which is at about 1.5 Mbits/sec. The video CD can also record some playback control data for interactive operation when the programs are played back.
FIG. 1 shows the data structure of a program that contains both audio and video information in a video CD. As illustrated, the video information is segmented and then formatted into video sectors (V) of the same length. The audio information is also segmented and then formatted into audio sectors (A). The video and audio sectors (V, A) are subsequently interleaved at about a 5:1 ratio to ensure real-time delivery when they are read during playback. It is not necessary to keep this ratio as long as no overflow or underflow occurs when the video CD is read. The interleaved video and audio sectors (V, A) constitute a program that may be logically called a file or a track in video CD terminology. The program may be a music video, a karaoke song, a movie, or an audio/video clip. There may be many files or tracks on a single video CD.
The video CD can be used to store only compressed audio programs. Compared to the original CD digital audio, this offers the potential of permitting the CD medium to store more audio data bits, i.e. about six times that of the original CD digital audio with comparable quality, and with the interactive capability. However, problems arise when only compressed audio programs are recorded on a video CD due to the fact that the compressed audio bit rate is much lower than the constant linear velocity of the CD drive. An arrangement, like that shown in FIG. 2, utilizes stuffing sectors (S) that are interleaved with the audio sectors (A) so that a total bit rate equal to the constant linear velocity of the CD drive can be retained. While the arrangement of FIG. 2 resolves the problem of delivery rate, the recording capacity of the CD medium is used inefficiently. Another arrangement, such as that shown in FIG. 3, clusters all of the audio sectors (A) to ensure a high recording density. However, the arrangement of FIG. 3 requires the CD drive to alternate frequently between stalling and advancing states, and will consequently result in serious degradation of the CD drive.